Meeting Abstract
Crustaceans rely on a wide spectrum of innate immune mechanisms to maintain their physiological integrity in aquatic environments that teem with high densities of microorganisms (> 106 culturable bacteria and 108 viruses/mL seawater). A successful immune response requires recognition of a foreign microbe, often mediated by pattern recognition proteins or lectins, linked to a defensive response that can sequester, inactivate, degrade and/or externalize the microbe. Like the insects, crustaceans rely on interplay between clotting, production of antimicrobial proteins and melanization to prevent hemolymph loss and microbial spread at sites of injury. In response to injected gram-negative bacteria, crustacean hemocytes aggregate and rapidly move to the site of injection, where they sequester, but do not immediately inactivate or degrade the injected microbes. Some hemocyte aggregates and bacteria become trapped in the microvasculature of the gills and other tissues, where they are melanized by the prophenoloxidase cascade and eliminated at the molt. Several lines of evidence show that these trapped hemocyte aggregates interfere with the gill’s normal function in respiration, including decreased O2-uptake, impaired movement and reduced oxygenation of hemolymph, along with the disappearance of a pH change across the gill. Consistent with this observation, blue crabs injected with bacteria fatigue more rapidly than saline-injected controls in measures of performance on a treadmill. For crustaceans that live in microbially-rich, but oxygen-poor aquatic environments, there appear to be distinct tradeoffs based on the gill’s multiple roles in respiration, ion balance and immunity (NSF IOS-1147008).
